C#查询DNS的MX地址的代码

//C#查询DNS的MX地址的代码
namespace PAB.DnsUtils 
{
 using System;
 using System.Collections;
 using System.ComponentModel;
 using System.Runtime.InteropServices;
 
 public class DnsMx
 {
  public DnsMx()
  {
  }
  
  [DllImport("dnsapi", EntryPoint="DnsQuery_W", CharSet=CharSet.Unicode, SetLastError=true, ExactSpelling=true)]
  private static extern int DnsQuery([MarshalAs(UnmanagedType.VBByRefStr)]ref string pszName, QueryTypes wType, QueryOptions options, int aipServers, ref IntPtr ppQueryResults, int pReserved);
  
  [DllImport("dnsapi", CharSet=CharSet.Auto, SetLastError=true)]
  private static extern void DnsRecordListFree(IntPtr pRecordList, int FreeType);
  
  public static string[] GetMXRecords(string domain) 
  { 
   IntPtr ptr1=IntPtr.Zero ;
   IntPtr ptr2=IntPtr.Zero ;
   MXRecord recMx;
   
   if (Environment.OSVersion.Platform != PlatformID.Win32NT)
   { 
    throw new NotSupportedException();
   } 
   
   ArrayList list1 = new ArrayList();
   
   int num1 = DnsMx.DnsQuery(ref domain, QueryTypes.DNS_TYPE_MX, QueryOptions.DNS_QUERY_BYPASS_CACHE, 0, ref ptr1, 0);
   
   if (num1 != 0) { throw new Win32Exception(num1); }
   
   for (ptr2 = ptr1; !ptr2.Equals(IntPtr.Zero); ptr2 = recMx.pNext)
   {
    recMx = ( MXRecord) Marshal.PtrToStructure(ptr2, typeof(MXRecord));
    
    if (recMx.wType == 15)
    { 
     string text1 = Marshal.PtrToStringAuto(recMx.pNameExchange);
     list1.Add(text1);
    }
   }
   
   DnsMx.DnsRecordListFree(ptr2, 0);
   
   return (string[]) list1.ToArray(typeof(string));
  }
  
  private enum QueryOptions { DNS_QUERY_ACCEPT_TRUNCATED_RESPONSE = 1, DNS_QUERY_BYPASS_CACHE = 8, DNS_QUERY_DONT_RESET_TTL_VALUES = 0x100000, DNS_QUERY_NO_HOSTS_FILE = 0x40, DNS_QUERY_NO_LOCAL_NAME = 0x20, DNS_QUERY_NO_NETBT = 0x80, DNS_QUERY_NO_RECURSION = 4, DNS_QUERY_NO_WIRE_QUERY = 0x10, DNS_QUERY_RESERVED = -16777216, DNS_QUERY_RETURN_MESSAGE = 0x200, DNS_QUERY_STANDARD = 0, DNS_QUERY_TREAT_AS_FQDN = 0x1000, DNS_QUERY_USE_TCP_ONLY = 2, DNS_QUERY_WIRE_ONLY = 0x100 }
  
  private enum QueryTypes { DNS_TYPE_MX = 15 }
  
  [StructLayout(LayoutKind.Sequential)]
  private struct MXRecord 
  {
   public IntPtr pNext;
   public string pName;
   public short wType;
   public short wDataLength;
   public int flags;
   public int dwTtl;
   public int dwReserved;
   public IntPtr pNameExchange;
   public short wPreference;
   public short Pad;
  }
 } 
}
static void Main(string[] args) 
{
 string[] s= PAB.DnsUtils.DnsMx.GetMXRecords("microsoft.com");
 
 foreach (string st in s) Console.WriteLine("Server: {0}",st);
 
 Console.ReadLine();
}